As well known in the art, the power amplifier design requires high efficiency and high linearity. The efficiency of radio frequency power amplifier is generally defined as a ratio between a desired transmitted power and the total power from power supplies. Consequently, extensive efforts are made within the wireless industry for the means of enhancing efficiency. A little improvement in the efficiency of a power amplifier can make substantial profit available in a wireless communication system or terminal and cut the overall costs needed to operate the wireless communication infrastructure or terminal.
A high linearity with low interference and noise is also important for a radio frequency power amplifier and a whole wireless communication system. In a wireless communication system, antenna filter in a transmitter are one of the most important component to filter out the noise and interference to keep the transmitter meet the requirements for different regions and standards. However, with ever emerging frequency bands, the requirements of antenna filter is ever increasing and challenging to suppress the interference and noise generated from radio frequency power amplifiers. In this regard, with more and more frequency bands for the 4th generation communication (4G) and beyond, requirements for an antenna filter in a transmitter are ever higher to be achieved, which are very challenging to the existing filter technology. For example, co-site and co-existence require more and more challenge filters or interference filtering requirements. Some of the operating frequency bands (e.g. band 1#-41#) specified for the 4G LTE systems require a very tight transmitter antenna filtering. However it seems to be impossible to achieve the requirements by using only one antenna filter. Moreover, there are also some new frequency bands introduced into the LTE advanced which are not yet specified in detail so that are yet to be seen. These non-continuous frequency bands could also cause challenging filter requirements.
In view of this, it is highly desired to alleviate the requirements of transmitter antenna filter from a side of a radio frequency power amplifier, rather than antenna filters design, to minimize the interference and noise generated from a radio frequency power amplifier.